Crystal habit modification of inorganic salts using polymeric sulfonates or sulfates

ABSTRACT

Disclosed herein is an improved method for crystallizing watersoluble inorganic salts. The improvement comprises adding to the crystallizing system a small amount of a monovalent salt of a polymeric sulphonate or sulfate characterized by the formula:   WHEREIN R is hydrogen or methyl, m is an integer from 3 to 3,000, n is 0 or 1, and Y is a connecting group which is oxo, phenyl, phenoxy, carboxy alkyl or similar organic radical. The X portion of the sulphonate or sulfate group is a monovalent cation such as hydrogen, lithium, sodium, potassium and ammonium. The resulting crystals are larger and more regularly shaped than crystals produced by prior art methods.

United States Patent [191 Teot [ Nov. 6, 1973 CRYSTAL HABIT MODIFICATION OF INORGANIC SALTS USING POLYMERIC SULFONATES OR SULFATES [21] Appl. No.: 119,396

' 52 us. Cl. .[23 300, 423/551 [51] Int. Cl B01d 9/02 [58] Field of Search .i 23/300, 121

I [56] References Cited UNITED STATES PATENTS 2,226,101 12/1940 Ogden 23/300 2,642,335 6/1953 May et a1 23/300 2,720,446 10/1955 Whetstone et a1... 23/300 3,037,849 6/1962 Frintet al. 23/300 3,248,182 4/1966 Herink et al 23/300 3,271,106 9/1966 Nylander 23/121 OTHER PUBLICATIONS Buckley, Crystal Growth (Wiley & Sons, New York, 1951), pp. 373377.

Whetstone, Modification of Crystal Habit of Inorganic Salts with Dyes, Nature, Vol. 168 No. 4276. p. 663-664 (1951) Primary Examiner-Norman Yudkoff Assistant Examiner-R. T. Foster AtmrneyGriswold & Burdick, Stephen S. Grace and Lloyd S. Jowanovitz ABSTRACT Disclosed herein is an improved method for crystallizing water-soluble inorganic salts. The improvement comprises adding to the crystallizing system a small amount of a monovalent salt of a polymeric sulphonate or sulfate characterized by the formula:

wherein R'is hydrogen or methyl, m is an integer from 3 to 3,000, n is 0 or 1, and Y is a connecting group which is oxo, phenyl, phenoxy, carboxy alkyl or similar organic radical. The X portion of the sulphonate or sulfate group is a monovalent cation such as hydrogen, lithium, sodium, potassium and ammonium. The resulting crystals are larger and more regularly shaped than crystals produced by prior art methods.

4 Claims, No Drawings CRYSTAL HABIT MODIFICATION OF INORGANIC SALTS USING POLYMERIC SULFONATES OR SULFATES' BACKGROUND OF THE INVENTION In the art of crystal habit modification, it is known that sulphonated alkyl diphenyl ether surfactants can sometimes be employed to modify crystallization of specific inorganic salts from an aqueous media (e.g., Nylander U.S. Pat. No. 3,271,106). Also polyacrylic acid and its salts, e.g., sodium polyacrylate, have been employed as crystal modifiers. Where successful, the crystals produced from the sulphonate containing media are larger, more uniform and/or possess a more desirable shape than is the case where crystallization is allowed to proceed naturally. For example, the crystal bulk density is increased for more economical shipping. Also, larger crystals have improved filterability. Unfortunately, the mechanism by which crystal modification is achieved is not well understood and, as a result, success or failure of a particular crystal modification technique is highly empirical.

1 The present invention-is based upon the discovery that monovalent polymeric sulphonates or sulfates of the prescribed formula improve crystallization of water-soluble inorganic salts such as (NI- 80 KNO KCl and K 80 from their respective aqueous solutions.

SUMMARY OF THE INVENTION In the present invention, a small amount of the poly- I meric sulphonate or sulfate is added to an aqueous solution of a water-soluble inorganic salt. Crystallization of the salt is then brought about by conventional means such as evaporation of the solvent, or cooling, or a combination of both methods. The resulting crystals are both larger and/or more symmetrical than if crystallization had been allowed to proceed without incorporation of the sulphonate or sulfate into the crystallization media. This permits, among otherthings,.easier filtration of such crystals.

.Inthe crystallization process, the amount of sulpho-' nate or sulfate employed is from about 0.0005 to about 0.5 weight percent of the amount of inorganic salt solubilized prior to the beginning-of crystallization. Preferably, the amount of sulphonate or sulfate employed is from about 0.005 to about 0.1 percent by weight of the inorganic salt.

The polymeric sulphonate or sulfate is characterized by the formula:

radical. The X portion of the sulphonate group is a' monovalent cation. Suitable ions include hydrogen, lithium, sodium, potassium and ammonium.

Suitable monovalent salts of sulphonates and sulfates are, for example, polystyrene sulfonate, polysulfoethyl methacrylate, polyvinylsulfonate, polyvinylsulfate, polyvinyltoluene sulfonate, polyallyl sulfate, vinyl phenyl ether sulfonate, polyvinylbenzyl sulfonate. Polymeric compounds with a molecular weight of from about 300 to about 1,000,000 can be employed.

Preferably, in carrying out the crystallization process of the invention, water, sulphonate or sulfate and the inorganic salt are admixed. The mixture is heated sufficiently to solubilize the reagents, and the resulting solution is filtered to remove any solid material. The mixture is then allowed to cool slowly to about C. over a period of several hours during which time crystal formation occurs.

A particular group of water-soluble, monovalent inorganic salts which are modified by the polymeric compounds disclosed are those relating to fertilizer production: ammonium sulfate, potassium nitrate, potassium chloride and potassium sulfate.

The following examples are submitted to illustrate the invention:

EXAMPLE I The following materials were charged into a large beaker: 1,400 grams of deionized water, 254.2 grams of K and 5 grams of a 1 percent (by weight) aqueous solution of sodium polystyrene sulphonate (SPSS) (molecular weight: 30,000).

The sulphonate present was about 0.02 percent by weight of the potassium sulfate. The mixture was heated to boiling and was filtered through a two micron filter into a 2 liter flask. The flask was placed in a large heated water bath. The mixture was agitated-slowly as the temperature was allowed to decrease gradually to room temperature. The cooling rate was about 8/hour and the time required for cooling was about 4.1 hours.

The K 80 crystallized in the form of large rhombohedrons without fines or rods.

EXAMPLE 11 Similar results were obtained when 0.1 percent (0.002 percent of sulfonate based on K 80 SPSS of a higher molecular weight, i.e., 780,000 was added to solution of 273 grams of K SO in 1,500 grams of H 0 and the solution crystallized as above. In the absence of the sulphonate, the K 80 crystallizes as a mixture of poorly formed rhombohedrons, rods of various sizes, twined crystals and fines.

EXAMPLE III Using KNO as the salt (1,100 grams KNO; in 1,000 grams H O), crystallization was carried out under conditions substantially similar to those in Example I. The concentration of sulphonate, however, was about 0.001 percent based on the weight of the KNO The KNO crystallized as a triclinic form with rounded edges. Without the sulfonate addition, KNO crystals contained a number of smaller, malformed triclinic crystals.

EXAMPLE IV Using KC] as the salt (637 grams KCl .in 1,400 grams H O), crystallization was carried out under conditions substantially similar to those in Example I. The concentration of sulphonate, however, was about 0.001 percent based on the weight of the RC1. The KCl crystals changed from a normal cubic habit to a rounded orthohombic shape.

EXAMPLE V Using copper sulfate as the salt (684 grams CuSO -5- H O in 1,100 grams H O), crystallization carried out under conditions substantially similar to Example I. The concentration of the sulfonate was about 0.015 percent based on the weight of CuSO '5H O. The crystals formed were larger than those produced without the addition of SPSS.

EXAMPLE VI Using potassium chromate as the salt (960 grams K CrQ, in 1,400 grams H O), crystallization was carried out under conditions substantially similar to Example I. The concentration of the sulphonate was 0.002 percent based on the weight of K CrO The crystals formed were larger than those produced without the addition of SPSS.

EXAMPLE v11 EXAMPLE VIII The same experiments were carried out as in Example Vll using sodium polysulfoethylmethacrylate instead of SPSS. Similar results in crystal modification were observed.

I claim:

1. In a process for crystallizing water-soluble inorganic salts from an aqueous system, the improvement, which comprises, crystallizing said salt from said aqueous system in the presence of a small amount of a monovalent inorganic salt of polymeric sulphonate or sulfate having a molecular weight ranging from about 300 to about l,000,000 selected from the group consisting of polystyrene sulfonate, polysulfoethyl methacrylate, polyvinylsulfonate, polyvinylsulfate, polyvinyltoluene sulfonate, polyallyl sulfate, vinyl phenyl ether sulfonate and polyvinylbenzyl sulfonate.

2. The process as in claim 1 wherein the water soluble inorganic salt is selected from the group consisting of potassium nitrate, potassium sulfate, potassium chloride, and ammonium sulfate.

3. A process as in claim 1 wherein from about 0.0005 to about 0.5 weight percent of polymeric sulphonate or sulfate is present in the aqueous system based on the weight of inorganic salt present therein.

4. A process as in claim 2 wherein the polymeric sulphonate is sodium polystyrene sulfonate or sodium polysulfoethylmethacrylate. 

2. The process as in claim 1 wherein the water soluble inorganic salt is selected from the group consisting of potassium nitrate, potassium sulfate, potassium chloride, and ammonium sulfate.
 3. A process as in claim 1 wherein from about 0.0005 to about 0.5 weight percent of polymeric sulphonate or sulfate is present in the aqueous system based on the weight of inorganic salt present therein.
 4. A process as in claim 2 wherein the polymeric sulphonate is sodium polystyrene sulfonate or sodium polysulfoethylmethacrylate. 